The common use of video cassette recorders, players and cameras in the world today has led to a need for the maintenancing and servicing of such video equipment. Generally, the first attempts at servicing video cassette equipment provided attempts at blocking sensors with black tape or holding or taping safety switches within the video equipment. Attempts were also made to remove the internal mechanisms of the video tape cassette so that the shell of the video tape cassette could be utilized to activate some of the sensors and safety switches of the video equipment. Still, not all safety switches and sensors were activated, and the shell of the video tape cassette blocked many of the internal working mechanisms of the video equipment so that the technician could not view the internal mechanisms of the video equipment when in the operating mode. Today, service cassettes provide a frame structure that is similar to or identical to the frame structure of a conventional video tape cassette while providing an open center portion so that a technician can easily view the internal mechanisms of the video equipment.
Still, the frame structure of the service cassettes did not actuate and engage sensors within the video equipment that were mounted beyond the frame structure of the service cassette. One such sensor is a tension pole that engages the magnetic video tape of a conventional video tape cassette. The tension pole is connected to the end of a tension arm, and the other end of the tension arm is pivotally connected to a chassis of the video equipment, adjacent to the video tape cassette. The tension pole contacts the magnetic video tape beyond the frame structure of the video tape cassette and pushes the magnetic video tape outward by pivoting at the chassis of the video equipment. The tension arm is spring biased away from the video tape cassette to provide the proper tension on the magnetic video tape.
The tension arm is also connected to a tension band which wraps around a supply reel of the video equipment and is fixedly anchored to the chassis of the video equipment. The supply reel, in combination with a take-up reel of the video equipment, engage two spools of a conventional video tape cassette that hold and wind the magnetic video tape in the conventional video tape cassette. When the tension pole engages the magnetic video tape, slack is provided in the tension band to allow the supply reel to rotate. When the magnetic video tape is not present, the tension arm is free to swing away from the video cassette tape wherein the tension arm tightens the tension band and prohibits the supply reel from rotating. Since the tension pole engages the magnetic video tape beyond the frame structure of the service cassette, the service cassette does not engage the tension pole, and therefore, the tension band prohibits the supply reel from rotating and prohibits a technician from observing the continuous operation of the video equipment. The service cassette cannot be made larger to engage the tension pole since the service cassette would be larger than a conventional video tape cassette and, therefore, would not accurately simulate the use of a conventional video tape cassette.
All of the video cassette recorders, players and cameras produced by various manufacturers utilize common formats and standard size video tape cassettes even though the internal mechanisms within the video equipment which interact with the video tape cassette are designed somewhat differently from manufacturer to manufacturer. One such internal mechanism that is designed differently from manufacturer to manufacturer is a photodetector that determines the presence and absence of the magnetic video tape of the conventional video tape cassette. The magnetic video tape is normally provided with a clear leader and a clear trailer, each of which are several inches in length. The clear leader and trailer portions have the same general dimensions and flexibility as the other portions of the tape but lack the magnetic recording material, such as a ferrous oxide coating, normally found on the rest of the video tape. The clear leaders and trailers are substantially transparent and therefore allow light to shine therethrough, while the other portions of the video tape containing magnetic recording material are substantially opaque and block a beam of light. The presence or absence of the transparent leader or trailer is detected by one of two photodiodes spaced apart from one another and located next to the tape cassette handling mechanism within a video cassette recorder, player and camera and are used to tell the video equipment when to start and stop in the various modes of operation.
Generally, all video cassette recorder manufacturers provide such a photodetector to determine the presence of the beginning and the end of the magnetic video tape of a conventional video tape cassette, but not all video equipment manufacturers mount the photodetector in the same location. Most video cassette recorder manufacturers mount the photodetector adjacent to the conventional video cassette tape, and therefore, the frame structure of the service cassette will block the light to the photodetector thereby actuating the photodetector and sending the proper signal to the video equipment to allow the video equipment to perform the play and record functions. When the photodetector is mounted beyond the frame structure of the service cassette, the service cassette will not block the light source to the photodetector, and therefore, the correct signal is not sent to the video equipment. As previously mentioned, the service cassette cannot be made larger to engage the additional photodetector since the service cassette would be larger than a conventional video tape cassette and, therefore, would not accurately simulate the use of a conventional video tape cassette.